An anaerobic organism or anaerobe is an organism that does not require oxygen to grow, may react adversely to the presence of oxygen and, if particularly sensitive, may die if exposed to a small amount of oxygen.
Since air consists of approximately 20% oxygen and 80% nitrogen, it is essential to cultivate anaerobes in a sealed vessel whose environmental conditions are controlled.
An anaerobic workstation is typically used to cultivate anaerobes. Anaerobic workstations comprise a sealed chamber and means to regulate the atmosphere, temperature and humidity as required. Anaerobe samples or cultures can be introduced, manipulated, incubated and examined in an anaerobic workstation without disturbing the environmental conditions and without exposing the anaerobes to atmospheric oxygen until they are removed from the anaerobic workstation.
Anaerobic workstations are suitable for use in a number of different industries and applications. For example, anaerobic culture stations are used in microbiology laboratories where there is a need to easily process, culture and examine microbiological samples without exposure to atmospheric oxygen.
An anaerobic workstation is supplied with an anaerobic gas mixture so as to provide an anaerobic atmosphere. The anaerobic gas mixture includes hydrogen gas. The hydrogen gas is provided to help to create and maintain the anaerobic conditions by combining with any oxygen in the atmosphere of the workstation. The hydrogen combines with oxygen in the presence of a catalyst. During the catalytic reaction, the hydrogen and oxygen combine in a ratio of 2:1 so as to form water vapour. The catalytic reaction is an exothermic reaction.
An anaerobe sample stored within an anaerobic workstation may be irreplaceably lost if the anaerobic atmosphere of the workstation is compromised. So as to maintain the stringent anaerobic conditions, it is necessary to ensure the ratio of hydrogen to oxygen is at least 2:1 and the catalyst is an active catalyst; i.e. a catalyst that has the efficacy (capacity) to initiate a catalytic reaction that is sufficient to remove any oxygen present in the workstation.
It is known and understood that the catalyst of an anaerobic workstation may degrade during use. This has the effect of slowing the rate of catalytic reaction and thereby the rate at which oxygen is removed from the workstation. The rate at which heat is generated during the sluggish catalytic reaction is also correspondingly reduced. If the catalyst fails during use then no catalytic reaction can occur to remove oxygen and the anaerobic conditions of the anaerobic workstation are therefore comprised. Accordingly, the catalyst is regularly replaced in anaerobic workstations so as to try and avoid degradation or failure of the catalyst.
So as to determine if the anaerobic condition is being maintained, anaerobic workstations may additionally comprise means to sense the presence or absence of oxygen. For example, control organisms may be utilized to confirm whether or not appropriate anaerobic conditions exist in an anaerobic workstation. Sensitive organism that will only grow in the absence of oxygen may be used as a positive control. Conversely, organisms that require the presence of oxygen to flourish may be used as a negative control. Control organisms provide an accurate and consistent confirmation that appropriate anaerobic conditions exist or have been compromised. However, there is often an undesirable time lag between a detectable result to alert a workstation user that the anaerobic atmosphere has been lost and this time lag may lead to the loss of samples. Moreover, the use of control organisms is labour intensive and can be expensive.
Others methods of detecting the atmosphere of an anaerobic workstation include the use of gas sensing means. For example, an anaerobic workstation may be provided with an oxygen sensor. Gas sensors are capable of reliable operation and rapidly detect the presence or absence of a gas. However, oxygen sensors that are capable of detecting the presence or absence of very low levels of oxygen can be expensive, can be adversely affected by the presence of other gases and/or compounds present in anaerobic environments, or experience unacceptable levels of drift thereby affecting accuracy over time.